A human eye can suffer diseases that impair a patient's vision. For instance, a cataract may increase the opacity of the lens, causing blindness. To restore the patient's vision, the diseased lens may be surgically removed and replaced with an artificial lens, known as an intraocular lens, or IOL. An IOL may also be used for presbyopic lens exchange.
The simplest IOLs have a single focal length, or, equivalently, a single power. Unlike the eye's natural lens, which can adjust its focal length within a particular range in a process known as accommodation, these single focal length IOLs cannot generally accommodate. As a result, objects at a particular position away from the eye appear in focus, while objects at an increasing distance away from that position appear increasingly blurred.
An improvement over the single focal length IOLs is an accommodating IOL, which can adjust its power within a particular range. As a result, the patient can clearly focus on objects in a range of distances away from the eye, rather than at a single distance. This ability to accommodate is of tremendous benefit for the patient, and more closely approximates the patient's natural vision than a single focal length IOL.
When the eye focuses on a relatively distant object, the lens power is at the low end of the accommodation range, which may be referred to as the “far” power. When the eye focuses on a relatively close object, the lens power is at the high end of the accommodation range, which may be referred to as the “near” power. The accommodation range or add power is defined as the near power minus the far power. In general, an accommodation range of 2 to 4 diopters is considered sufficient for most patients.
The human eye contains a structure known as the capsular bag, which surrounds the natural lens. The capsular bag is transparent, and serves to hold the lens. In the natural eye, accommodation is initiated in part by the ciliary muscle and a series of zonular fibers, also known as zonules. The zonules are located in a relatively thick band mostly around the equator of the lens, and impart a largely radial force to the capsular bag that can alter the shape and/or the location of the natural lens and thereby change its effective power.
In a typical surgery in which the natural lens is removed from the eye, the lens material is typically broken up and vacuumed out of the eye, but the capsular bag is left intact. The remaining capsular bag is extremely useful for an accommodating intraocular lens, in that the eye's natural accommodation is initiated at least in part by the zonules through the capsular bag. The capsular bag may be used to house an accommodating IOL, which in turn can change shape and/or shift in some manner to affect the power and/or the axial location of the image.
The IOL has an optic, which refracts light that passes through it and forms an image on the retina, and a haptic, which mechanically couples the optic to the capsular bag or holds the IOL in contact with the capsular bag. During accommodation, the zonules exert a force on the capsular bag, which in turn exerts a force on the optic. The force may be transmitted from the capsular bag directly to the optic, or from the capsular bag through the haptic to the optic.
One challenge in implementing an accommodating optic is designing a suitable haptic to couple the optic to the capsular bag. The haptic should allow distortion of the optic in an efficient manner, so that a relatively small ocular force from the ciliary muscle, zonules, and/or capsular bag can produce a relatively large change in power and/or axial location of the image. This reduces fatigue on the eye, which is highly desirable.
Accordingly, there exists a need for an intraocular lens having a haptic with increased efficiency in converting an ocular force to a change in power and/or a change in axial location of the image.